Differential Detection unit for the Zigbee 802.15.4 Standard

ABSTRACT

In one embodiment, a detection unit includes a sequence providing unit to provide a third group of derived sequences. The third group for each first pseudo noise (PN) sequence has a derived sequence assigned to the first PN sequence. The detection unit includes a correlation unit, which is connected to the sequence providing unit and formed to calculate correlation results by correlating the differentially demodulated signal with each derived sequence of the third group. The detection unit includes an evaluation unit, which is connected to the correlation unit and is formed to derive the values of the data symbols by evaluating the correlation results.

The present invention relates to a detection unit for detecting datasymbols contained in a differentially demodulated signal. The inventionrelates furthermore to a transmitting/receiving device and to anintegrated circuit with such a detection unit.

The invention falls within the field of data transmission. Although itcan be used in principle in any digital communication system, thepresent invention and its underlying problem will be explained belowwith reference to a “ZigBee” communication system in accordance withIEEE 802.15.4.

So-called “Wireless Personal Area Networks” (WPANs) can be used for thewireless transmission of information over relatively short distances(about 10 m). In contrast to “Wireless Local Area Networks” (WLANs),WPANs require little or even no infrastructure for data transmission, sothat small, simple, energy-efficient, and cost-effective devices can beimplemented for a broad range of applications.

Standard IEEE 802.15.4 specifies low-rate WPANs, which are suitable withraw data rates up to a maximum of 250 kb/s and stationary or mobiledevices for applications in industrial monitoring and control, in sensornetworks, in automation, and in the field of computer peripherals andfor interactive games. In addition to a very simple and cost-effectiveimplementability of devices, an extremely low power requirement ofdevices is of critical importance for such applications. Thus, anobjective of this standard is a battery life of several months toseveral years.

At the level of the physical layer, in the virtually globally available2.4 GHz ISM band (industrial, scientific, medical) for raw data rates offB=250 kbit/s, the IEEE standard 802.15.4 specifies a band spread(spreading) with a chip rate of fC=2 Mchip/s and an offset QPSKmodulation (quadrature phase shift keying) with a symbol rate of fS=62.5ksymbol/s.

In an 802.15.4 transmitter for the ISM band, the data stream to betransmitted is first converted to a sequence of PN sequences (pseudonoise) with the use of four data bits in each symbol period (TS=1/fS=16μs), in order to select a PN sequence for a sequence set of a total of16 PN sequences. Each symbol of four data bits is assigned in thismanner a symbol value-specific PN sequence from 32 PN Chips (chip periodTC=TS/32=500 ns=1/fC), which is transmitted instead of the four databits. The sequence set of 16 “quasi-orthogonal” PN sequences, specifiedin the standard, in this case comprises a first group of eight first PNsequences, which differ from one another only by a cyclic shift of theirchip values, and a second group of eight second PN sequences, which alsodiffer from one another only by a cyclic shift of their chip values andfrom one of the first PN sequences only by an inversion of each secondchip value (see IEEE Standard 802.15.4-2003, Chapter 6.5.2.3).

The PN sequences assigned to the successive symbols are linked togetherand then offset QPSK modulated (quadrature phase shift keying) bymodulating, with half-sine pulse shaping, the even-indexed PN chips (0,2, 4, . . . ) onto the in-phase (I) carrier and the odd-indexed PN chips(1, 3, 5, . . . ) onto the quadrature-phase (Q) carrier. To form anoffset, the quadrature-phase chips are delayed by a chip period TC withrespect to the in-phase chips (see IEEE Std 802.15.4-2003, Chapter6.5.2.4).

Both coherent and incoherent approaches are known per se receiver-sideto detect data symbols present in an incoming signal. Whereas incoherent approaches the incoming signal is converted into the complexenvelope (baseband) with use of a carrier wave of the same frequency andphase and obtained from a carrier control circuit, in incoherentapproaches at least the appropriates of the phase, within limitspossibly also the appropriateness of the frequency of the carrier wave,can be dispensed with. Because of the higher realization cost incoherent approaches, which is also associated with an increased powerrequirement, in the current invention an incoherent receiver is used inwhich the incoming signal is converted at least not in-phase into thecomplex envelope and the resulting baseband signal is demodulateddifferentially.

Furthermore, it is known per se to multiply the data symbols fromseveral communication participants transmit-side in each case with aparticipant-specific PN sequence from a sequence set of orthogonal PNsequences, to transmit the composite signal, and to detect receiver-sidethe data symbols of a specific participant in that the receivedcomposite signal is correlated with the PN sequence of this participantand subsequently decided. References is made in this regard, e.g., tothe textbook “Nachrichtenübertragung” [Message Transmission] byKarl-Dirk Kammeyer, 3^(rd) edition, B. G. Teubner, Stuttgart, ISBN3-519-26142-1 (pages 632-635).

In view of this background, the object of the invention is to provide adetection unit for detecting data symbols contained in a differentiallydemodulated signal that enables energy-efficient and simpleimplementation of transmitting/receiving devices, e.g., according toIEEE 802.15.4, and yet has a high detection efficiency, i.e., a lowerror rate (symbol, bit, frame error rate, etc.) also with interferenceeffects such as channel distortions and/or noise. It is furthermore theobject of the invention to provide a suitable transmitting/receivingdevice and an integrated circuit.

This object is achieved according to the invention by a detection unit,a transmitting/receiving device, and an integrated circuit with thefeatures of claims 1, 22, and 23, respectively.

Accordingly, provided are: a detection unit for detecting data symbolswhich are contained in a differentially demodulated signal and to whichtransmit-side in each case a PN sequence from a sequence set can beassigned, which has a first group of first PN sequences and a secondgroup of second PN sequences, whereby the first and second PN sequenceswithin their respective group differ from one another only by a cyclicshift in their chip values and whereby the second group for each firstPN sequence has a corresponding second PN sequence, which differs fromthe first PN sequence only by an inversion of each second chip value,comprising a) a sequence providing unit, which is formed to provide athird group of derived sequences, whereby the third group for each firstPN sequence has a derived sequence, which is assigned to said first PNsequence and can be derived therefrom by means of logic operations, butis not identical thereto, and whereby the derived sequences of the thirdgroup differ from one another only by a cyclic shift of their chipvalues, b) a correlation unit which is connected to the sequenceproviding unit and is formed to calculate correlation results bycorrelating the differentially demodulated signal with each derivedsequence of the third group, and c) an evaluation unit which isconnected to the correlation unit and is formed to derive the values ofthe data symbols by evaluating the correlation results.

The transmitting/receiving device of the invention and the integratedcircuit of the invention each have this type of detection unit.

The essence of the invention is to provide a third group of derivedsequences adapted to the differential demodulation and to correlate thedifferentially demodulated signal with each derived sequence of thethird group. The derived sequences of the third group are not identicalto the PN sequences usable transmit-side—but derived therefrom—anddiffer from one another—in contrast to the PN sequences usabletransmit-side—only by a cyclic shift of their chip values. This makes itpossible to correctly detect (decide) a differentially demodulatedsignal generated transmit-side, e.g., according to IEEE 802.15.4. Inaddition, the particular properties of the derived sequences enableextremely simple and energy-efficient implementations of the detectionunit and thereby the transmitting/receiving devices.

This is advantageous particularly when—as in applications in industrialmonitoring and control, sensor networks, and automation, or in the fieldof computer peripherals—an extremely low power requirement and a verysimple realizability are indispensable. Although the invention is notlimited to the IEEE standard 802.15.4, this is the case for thisstandard by way of example in transmitting/receiving devices.

The efficiency of the detection unit of the invention is very high.Thus, the error rate (symbol, bit, frame error rate, etc.) duringdetection is very low according to simulations performed by theapplicant also under interfering effects such as channel distortions andnoise.

Advantageous embodiments and developments of the invention are to bederived from the dependent claims and from the description withreference to the drawing.

In an advantageous embodiment, the sequence providing unit has preciselyone memory means, which is formed to store precisely one (i.e., onlyone) of the derived sequences. A memory means, whose size is dimensionedin this way, can be advantageously very simply implemented and operatedwith saving of power.

The memory means preferably is made hereby as a feedback shift register.The very simple structure of a shift register of series-connectedregister cells makes possible a very efficient and simple realization ofthe sequence providing unit with a very low power requirement. Thus,e.g., neither calculation of memory addresses nor a complex controllogic is required for the shift register.

The sequence providing unit hereby preferably provides the derivedsequences of the third group at the outputs of the respective (several)register cells of the shift register. For this purpose, means areprovided for clocking the feedback shift register in the chip clock. Allderived sequences of the third group with or without a time offset amongeach other can be provided very simply in this way.

In another advantageous embodiment, the sequence providing unit has acounting unit and multiplexer connected thereto, whereby fixed valuescan be applied at the inputs of the multiplexer and the sequenceproviding unit is formed to provide the derived sequences of the thirdgroup at the outputs of the multiplexers. This type of structurecomprising logic elements also makes possible a very efficient andsimple realization of the sequence providing unit with a very low powerrequirement.

In another embodiment, the number n of the at least two derivedsequences of the third group corresponds to the number the first PNsequences in the first group and this in turn to the number of thesecond PN sequences in the second group. Thereby, the number of thederived sequences of the third group is only half as high as the numberof the overall usable PN sequences transmit-side. This advantageouslymakes possible a simpler realization particularly of the correlationunit but also of the sequence providing unit and of the evaluation unit.

The correlation unit preferably comprises n multiplier units and ndownstream integration units, whereby the multiplier units, eachconnected to the sequence providing unit and the differentialdemodulator (or equalizer), calculate n product signals by multiplying(individually delayed or not delayed and present in the chip clock)signal values of the demodulated (and optionally equalized) signal by(optionally also higher-level [more than two-level]) chip values in eachcase of one of the derived sequences of the third group, and then eachintegration unit per symbol period provides a correlation result byadding a number of signal values of the corresponding product signal.This type of realization of the correlation unit is very simple,requires very little operating energy, and enables a high efficiency inthe detection error rate.

If the derived sequences of the third group have two-level chip values(e.g., +/−1), the multiplier units can be realized advantageously asextremely simply constructed means for sign reversal.

Preferably, one chip value of each derived sequence is not considered inthe correlation calculation. Despite the differential demodulation, twosuccessive data symbols can be advantageously decided independent of oneanother in this way.

According to another embodiment, the evaluation unit evaluates in aparallel manner the n correlation results per symbol period byevaluating them substantially simultaneously, i.e., during one chipperiod or during a few chip periods of each symbol period. In this way,the results of the correlation result evaluation are completelyavailable as early as possible, so that the decisions about the datasymbol values transmitted with the greatest probability can be madeadvantageously in each case as early as possible.

Preferably, the evaluation unit comprises a parallel maximum valuedetermination unit and a downstream allocation unit, whereby theparallel maximum value determination unit, connected to the integrationunits of the correlation unit, compares the n correlation results withone another in amount per symbol period substantially simultaneously,i.e., during one chip period or during a few chip periods of each symbolperiod, and determines as the result the signed value of themaximum-value correlation result and a sequence index with valuesbetween 0 and n-1, which indicates which of the n derived sequences ofthe third group is to be assigned to this signed value, and whereby theallocation unit determines a value of one of the data symbols from thesequence index and the sign of the signed value of the maximum-valuecorrelation result. An evaluation unit, which provides decisions on datasymbol values as early as possible, can be implemented simply and energyefficiently in this way.

According to a preferred embodiment, in which the third group comprisesat least four derived sequences, the correlation unit has delayelements, which are arranged in such a way that per symbol period twofirst results of the correlation results are provided in the same chipperiod and n-2 second results of the correlation results in followingchip periods. The evaluation unit in this case evaluates serially the ncorrelation results per symbol period by evaluating the firstcorrelation results during a first chip period and one each of thesecond correlation results during the following chip periods. Theevaluation unit can be constructed more simply due to the serialprovision and evaluation of the correlation results each time insuccessive chip periods. In addition, the operating energy is consumedmore uniformly over time or fewer peak currents occur in comparison withthe parallel implementation. This is advantageous both with respect tointerfering radiation and in regard to the battery lifetime.

Preferably, the delay elements in this case are arranged in the signalpath upstream of the multiplier units, because in this way the delay ofthe correlation results is achieved with the lowest possible (hardware)effort.

The evaluation unit preferably comprises a serial maximum valuedetermination unit and a downstream allocation unit. In this case, theserial maximum value determination unit during the first chip periodcompares the first correlation results in amount and determines as theresult the signed value of the first correlation result that has thehighest amount, and a sequence index which indicates which of thederived sequences of the third group is to be assigned to this signedvalue. During the following chip periods, the serial maximum valuedetermination unit compares one each of the second correlation resultsin amount with the result determined in each case during the precedingchip period and determines as the result the signed value that has thehighest amount, and a sequence index which indicates which of thederived sequences is to be assigned to this signed value. This step iscarried out so often until all second correlation results are consideredand thus the signed value of the maximum-value correlation result and asequence index (with values between 0 and n-1) are determined thatindicates which of the n derived sequences is to be assigned to thissigned value. The allocation unit finally determines a value of one ofthe data symbols from the sequence index and the sign of the signedvalue of the maximum-value correlation result. This evaluation unit isadvantageously constructed very simply, requires extremely little energyduring operation, and is notable for a high efficiency in detectionerror rate.

Preferably, the serial maximum value determination unit comprises afirst multiplexer, a second multiplexer, and a logic unit. The firstmultiplexer hereby has a first input, which is connected to a firstintegration unit of the correlation unit, and a second input, which isconnected to the first output of the logic unit. The second multiplexerhas n-1 inputs, which are connected to the n-1 remaining (“second”)integration units. The logic unit has two inputs, which are connected tothe two outputs of the two multiplexers, and two outputs. The firstmultiplexer is controlled in such a way that during the first chipperiod it conducts to its output the first correlation result applied atits first input and in the following chip periods the value applied atits second input, whereas the second multiplexer is controlled in such away that during the first chip period it conducts to its output thefirst correlation result applied at one of its inputs and in thefollowing chip periods one each of the second correlation resultsapplied at its other inputs. The logic unit in each case compares inamount the two values conducted by both multiplexers and determines thesigned value of the value higher in amount and the sequence index of thederived sequence to be assigned to this signed value. It provides thesigned value at the first output and the sequence index at the secondoutput. This serial maximum value determination unit is advantageouslyconstructed very simply. In addition, the operating energy is consumedmore uniformly over time or fewer peak currents occur in comparison withthe parallel implementation. This is advantageous both with respect tointerfering radiation and in regard to the battery lifetime.

Preferably, the allocation unit determines the value of one of the datasymbols that is assigned the first PN sequence of the first group thatis assigned the derived sequence with this sequence index (value), ifthe signed value of the maximum-value correlation result is positive,and otherwise the value of one of the data symbols that is assigned thesecond PN sequence of the second group that is assigned the sequenceinverse to the derived sequence with this sequence index (value). Thistype of allocation unit is advantageously constructed very simply andrequires extremely little power during operation.

In another embodiment, the derived chips (i.e., the chips of a derivedsequence) with a first positive index (i.e., all chips other than thefirst one) each have a value that can be derived from an XOR operationof the PN chip (i.e., the chip of the first PN sequence to which thederived sequence is assigned) with said first positive index with the PNchip preceding index-wise (and thereby in time). The first chip (withindex zero) derived index-wise (and in time) preferably has a value thatcan be derived from an XOR operation of the index-wise first PN chip(with index zero) with the index-wise last PN chip. The sequenceproviding unit, the correlation unit, and the evaluation unit can berealized very simply and with saving of power by using derived sequencesof this type.

The invention will be described in greater detail hereinafter with useof the exemplary embodiments shown in the schematic figures of thedrawing. Here,

FIG. 1 shows a “Wireless Personal Area Network” (WPAN) according to IEEEStandard 802.15.4 with transmitting/receiving devices (TRX) of theinvention;

FIG. 2 shows an incoherent receiving unit with a detection unit of theinvention 28;

FIG. 3 shows a first exemplary embodiment of a detection unit of theinvention;

FIG. 4 shows a preferred second exemplary embodiment of a detection unitof the invention; and

FIG. 5 shows a preferred realization form of the sequence providingunit.

In the figures, the same and functionally identical elements andsignals, if not specified otherwise, are provided with the samereference characters.

FIG. 1 shows an example of a “Wireless Personal Area Network” (WPAN) 10according to the IEEE standard 802.15.4. It comprises threetransmitting/receiving devices (transceiver, TRX) 11-13 in the form ofstationary or mobile devices, which exchange information in a wirelessmanner by means of radio signals. Transmitting/receiving device 11 is aso-called full-function device, which assumes the function of the WPANcoordinator, whereas transmitting/receiving devices 12, 13 are so-calledreduced-function devices, which are assigned to full-function device 11and can only exchange data with said device. Apart from the star networktopology depicted in FIG. 1, in which bidirectional data transmissioncan only occur between one of the reduced-function devices 12, 13 andthe full-function device 11, but not between the reduced functiondevices 12, 13, the standard also provides so-called “peer-to-peer”topologies, in which all full-function devices (of which one assumes therole of the WPAN coordinator) can communicate with all otherfull-function devices.

Transmitting/receiving devices 11-13 each comprise an antenna 14, atransmitting unit (transmitter, TX) 15 connected to the antenna, areceiving unit (receiver, RX) 16 connected to the antenna, and a controlunit (control unit, CTRL) 17, connected to the transmitting andreceiving unit, to control transmitting and receiving units 15, 16.Furthermore, transmitting/receiving units 11-13 each contain a powersupply unit, not shown in FIG. 1, in the form of a battery, etc., tosupply power to units 15-17, and possibly other components such assensors, interfaces, etc.

It will be assumed in the following text that the data transmissionoccurs in the 2.4 GHz ISM band (industrial, scientific, medical).Transmitting unit 15 of each transmitting/receiving device converts thedata stream to be transmitted in each case according to the IEEEStandard 802.15.4 into a radio signal to be emitted over its antenna 14by first converting the data stream to be transmitted in each case, asdescribed in the introduction to the description, to four bit widesymbols d0, d1, d2, . . . and these into successive PN sequences (e.g.,P5, P4, P7, if d0=5, d1=4, d2=7). The successive PN sequences are thenoffset QPSK modulated (quadrature phase shift keying) with half-sinuspulse formation.

Accordingly, receiving unit 16 of each transmitting/receiving deviceconverts a radio signal received from its antenna 14 (and generated bythe transmitting unit of another transmitting/receiving device accordingto the IEEE Standard 802.15.4) without errors if possible into thetransmitted data by demodulating the radio signal inter alia anddetecting (deciding) the data.

Transmitting unit 15 and receiving unit 16 of a transmitting/receivingdevice are hereby part of an integrated circuit (IC) (not shown in FIG.1), e.g., an ASICs (application specific integrated circuit), whereascontrol unit 17 is realized by means of a microcontroller (also notshown). Advantageously, the transmitting/receiving device can also haveonly one IC (e.g., made as an ASIC), which senses the functions oftransmitting unit 15, receiving unit 16, and control unit 17.

FIG. 2 shows a block diagram of an incoherent receiving unit (RX) 16,which comprises the following functional blocks connected in series: aninternal receiver (iREC) 21, a differential demodulator (DEMOD) 22, anda detection unit 28 of the invention, which has a correlation unit (COR)23 and a downstream evaluation unit (EVAL) 24, as well as a sequenceproviding unit (SEQ) 25 connected to correlation unit 23. In addition,receiving unit 16 optionally has an equalizer (EQ) 26 betweendemodulator 22 and detection unit 28.

Internal receiver 21 connected to antenna 14 of thetransmitting/receiving device converts the received radio signal r intoa complex baseband signal b (envelope), which has complex-valuedsampling values in the clock of the PN chips, used transmit-side, of thePN sequences; i.e., in chip clock fC=2 Mchip/s=1/TC=1/500 ns. Eachcomplex sampling value hereby comprises a real part (in-phase componentI) and an imaginary part (quadrature component Q). Complex-valuedsignals like the baseband signal b are shown in the figures by arrowswith double lines.

Internal receiver 21 furthermore has a synchronization unit (SYNC) 27,which carries out a symbol and chip clock synchronization.

The baseband signal b is then converted by differential demodulator 22into a demodulated signal, which has real-valued signal values in thechip clock fC. Advantageously, differential demodulator 22 generates ademodulated signal whose signal value has so-called soft informationvalues (higher level, e.g., 4-bit-wide signal values) instead of theso-called hard bits (i.e., two-level, binary values).

The demodulated signal is then optionally equalized. Equalizer 26provided for this purpose determines preferably per symbol periodTS=1/fS=16 μs=32*TC a mean of the demodulated signal and releases thissignal subsequently by subtracting the mean from a direct component.Alternatively or in addition, equalizer 26 may have a filter, e.g., ahigh-pass filter. The differentially demodulated (and optionallyequalized) signal is designated with an s hereafter.

Next, the data symbols d0, d1, d2, . . . , contained in thedifferentially demodulated (and optionally equalized) signal s, aredetected, i.e., decided, by detection unit 28 of the invention. For thispurpose, the signal s present in the chip clock fC (with, for example,four-bit-wide signal values) is first correlated in correlation unit(COR) 23 with so-called derived sequences F0, F1, . . . , F7, which areprovided by sequence providing unit 25. This leads to the correlationresults rsF0, rsF1, . . . , rsF7, which represent a measure for theconformity of the signal s with the particular derived sequence F0, F1,. . . , or F7. The correlation results are generated in the symbol clockfS=fC/32=62.5 ksymbol/s (corresponds to a symbol period of TS). Thecorrelation results rsF0, rsF1, . . . , rsF7 are finally evaluated inevaluation unit (EVAL) 24 and the data symbols d0, d1, d2, . . . aredetected (decided).

Due to detection unit 28 of the invention, which will be described ingreater detail hereinafter, transmitting/receiving devices 11-13 of FIG.1 are notable for a very simple realizability, a very low powerrequirement, and a high efficiency (bit error rate or the like dependingon interfering effects such as noise and/or channel distortions).

It will be described hereinafter how the derived sequences F0, F1, . . ., F7 provided by sequence providing unit 25 according to FIG. 2 areobtained. The following table shows both PN sequences P0, P1, . . . tobe used transmit-side according to IEEE 802.15.4 and also the derivedsequence F0, F1, . . . assigned to PN sequences of the invention.

In regard to the PN sequences P0, P1, P2, . . . to be usedtransmit-side, it must be determined first that a sequence set with atotal of 16 PN sequences P0, P1, . . . , P15 is specified. Each PNsequence in this case comprises 32 so-called chips, each of which canassume a value of logic zero (0) or one (1). As is evident from thetable, e.g., the first 10 chips of the PN sequence P5 assume the values0 0 1 1 0 1 0 1 0 0.

For the chips, e.g., of PN sequence P5, the parameters P5 c 0 (firstchip (c0) of P5), P5 c 1 (second chip (c1)), . . . , P5 c 30, P5 c 31(last chip (c31) are introduced to simplify the description. This alsoapplies to the other PN sequences, so that Picj designates the chip withindex j (i.e., the (j+1)-th chip) of the PN sequence with index i (Pi),whereby i=0, 1, . . . , 15 and j=0, 1, . . . , 31. Furthermore, tobetter differentiate the chips of the PN sequences from those of thederived sequences, the former are designated as PN chips.

If all 16 PN sequences P0, P1, . . . , P15 of the sequence set aredivided into a first group PG1 of the eight “first” PN sequences P0, P1,. . . , P7 and a second group PG2 of the eight “second” PN sequences P8,P9, . . . , P15, it is evident further from the table that the first PNsequences P0, P1, . . . , P7 differ from each other only by a cyclicshift of their chip values. Thus, e.g., the bit pattern {1 1 0 1 1 0},occurring at the start of the PN sequence P0, is evident—in a cyclicexpansion—in the PN sequence P1 starting at the PN chip P1 c 4, in thePN sequence P2 starting at P2 c 8, in P3 starting at P3 c 12, in P4starting at P4 c 16, . . . , and finally in P7 starting at P7 c 28. Thesecond PN sequences P8, P9, . . . , P15 as well differ from one anotheronly by a cyclic shift of the chip values.

P0: 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 F0: + + + − − − − − − + + + − + + +P1: 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 F1: + + − − + + + − − − − − − + + +P2: 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 F2: − + + − + + − − + + + − − − − −P3: 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 F3: + + + − − + + − + + − − + + + −P4: 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 F4: + − + − + + + − − + + − + + − −P5: 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 F5: − + + + + − + − + + + − − + + −P6: 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 F6: − + + + − + + + + − + − + + + −P7: 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 F7: − − − − − + + + − + + + + − + −P8: 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 F8: − − − + + + + + + − − − + − − −P9: 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 F9: − − + + − − − + + + + + + − − −P10: 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 F10: + − − + − − + + − −− + + + + + P11: 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 F11: − − − + + − − + −− + + − − − + P12: 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 F12: − + − + − −− + + − − + − − + + P13: 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 F13: + − − −− + − + − − − + + − − + P14: 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 F14: + − −− + − − − − + − + − − − + P15: 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0F15: + + + + + − − − + − − − − + − + P0: 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0F0: + − + − + + + − − + + − + + − − P1: 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0F1: − + + + + − + − + + + − − + + − P2: 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0F2: − + + + − + + + + − + − + + + − P3: 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1F3: − − − − − + + + − + + + + − + − P4: 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1F4: + + + − − − − − − + + + − + + + P5: 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0F5: + + − − + + + − − − − − − + + + P6: 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1F6: − + + − + + − − + + + − − − − − P7: 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1F7: + + + − − + + − + + − − + + + − P8: 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1F8: − + − + − − − + + − − + − − + + P9: 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1F9: + − − − − + − + − − − + + − − + P10: 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1F10: + − − − + − − − − + − + − − − + P11: 1 1 0 0 1 0 0 1 0 1 1 0 0 0 00 F11: + + + + + − − − + − − − − + − + P12: 1 0 0 0 1 1 0 0 1 0 0 1 0 11 0 F12: − − − + + + + + + − − − + − − − P13: 1 0 1 1 1 0 0 0 1 1 0 0 10 0 1 F13: − − + + − − − + + + + + + − − − P14: 0 1 1 1 1 0 1 1 1 0 0 01 1 0 0 F14: + − − + − − + + − − − + + + + + P15: 0 1 1 1 0 1 1 1 1 0 11 1 0 0 0 F15: − − − + + − − + − − + + − − − + Pi: PN sequence i(transmit-side) (Pic0 Pic1 Pic2 Pic3 . . . Pic30 Pic31) Fi: sequencederived from Pi (Fic0 Fic1 Fic2 Fic3 . . . Fic30 Fic31)

It is evident furthermore that for each first PN sequence of the firstgroup PG1 there is a second PN sequence of the second group PG2, whichdiffers from this first PN sequence of the first group PG1 only by everysecond chip value—namely, by an inversion of every second chip value.If, e.g., the PN sequences P0 from PG1 and P8 from PG2 in the table arecompared, it is found that the even-indexed PN chips have identicalvalues (P0 c 0=P8 c 0=1; P0 c 2=P8 c 2=0; P0 c 4=P8 c 4=1; etc.),whereas the odd-indexed PN chips assume different values (inverted toone another) (P0 c 1=1, P8 c 1=0, P0 c 3=1, P8 c 3=0; P0 c 5=0, P8 c5=1, etc.).

Each PN sequence according to the invention is assigned a nonidenticalderived sequence, matched to the differential demodulation, for example,the derived sequence F0, listed the table below P0, to the PN sequenceP0, the derived sequence F1 to the PN sequence P1, etc. The chips of thederived sequences, here designated as derived chips, can assume theantipodal values +1 and −1, whereby for reasons of clarity only the signof these values is entered in the table. In analogy to the designationfor the PN chips introduced above, the derived chip with the index j ofthe derived sequence with the index i is designated below with Ficj,whereby i=0, 1, . . . , 15 and j=0, 1, . . . , 31.

The values of the derived chips result as follows from the value of thePN chips. In order to form, e.g., the value of the derived chip F0 c 2,which according to the table is +1, the value of the PN chip P0 c 2=0,entered directly above in the table, is to be logically XORed with thevalue of the PN chip P0 c 1=1, entered to the left (i.e., preceding intime) of P0 c 2. The logic XOR operation in this case produces a valueof logic 1, which is assigned the antipodal value +1 entered in thetable for F0 c 2. Accordingly, the value of F0 c 4 from P0 c 4 XOR P0 c3=1 XOR 1=0 results for the value of −1 entered in the table for F0 c 4,because the logic zero is assigned an antipodal value of −1. Thisderivation rule applies to all derived chips with positive even index.If, therefore, Ficj designates the derived chip with the index j of thederived sequence with the index i and Picj and Picn the PN chip with theindex j or n of the PN sequence with the index i, for positive evenindexes j the derived chip Ficj for i=0, 1, . . . , 15 is given as

Ficj=2*(Picj XOR Picn)−1 with n=j−1 for j=2, 4, 6, . . . , 30,   (1)

whereby the multiplication of the result of the XOR operation with thefactor 2 and the subsequent subtraction of 1 is to reflect theassignment of the logic values of 0 and 1 to the antipodal values −1 or+1.

To form the derived chip Ficj with index j=0, the last PN chip Picn withn=31 is to be used instead of the (nonexistent) PN chip Picn, precedingin time, with index n=j−1=−1, i.e.,

Ficj=2*(Picj XOR Picn)−1 with j=0 and n=31 for i=0, 1, . . . , 15.   (2)

A derivation rule similar to equation (1) applies to the derived chipsFicj with the odd index j. In this case, the result of the XOR operationis to be inverted before the assignment to antipodal values:

Ficj=2*INV{Picj XOR Picn}−1 with n=j−1 for j=1, 3, 5, . . . , 31,   (3)

Here, INV{ } designates the logic inversion and i=0, 1, . . . , 15 againapplies.

Instead of the inversion of logic values with the subsequent assignmentof logic 0 to the antipodal value −1 and of logic 1 to the antipodalvalue +1, naturally also a different assignment can be used, namely oflogic 0 to the antipodal value +1 and of logic 1 to the antipodal value−1, and therefore the logic inversion can be omitted. The following thenresults as the formula

Ficj=1−2*(Picj XOR Picn) with n=j−1 for j=1, 3, 5, . . . , 31.   (3)

The use of the PN chip “current” in each case (with the index of thederived chip to be formed) and of the PN chip preceding in each casecorresponds to the transmit-side division, described in the introductionto the description, of the even-(odd-)indexed PN chips on thein-phase-(I) carrier (quadrature-phase (Q) carrier) within the scope ofthe offset QPSK modulation (quadrature phase shift keying). Othertransmit-side I/Q divisions of the PN chips require an appropriatelymatched formation of the derived chips.

If all 16 derived sequences F0, F1, . . . , F15 are divided into a thirdgroup FG1 of the eight derived sequences F0, F1, . . . , F7 and a fourthgroup FG2 of the eight derived sequences F8, F9, . . . , F15, it istherefore evident from the table that the derived sequences F0, F1, . .. , F7 of the third group FG1 differ from one another only by a cyclicshift of their chip values. Thus, e.g., the bit pattern {+++−−−},occurring at the start of the derived sequence F0, is evident—in acyclic expansion—in the derived sequence F1 starting at the derived chipF1 c 4, in the derived sequence F2 starting at F2 c 8, in F3 starting atF3 c 12, in F4 starting at F4 c 16, . . . , and finally in F7 startingat F7 c 28. The derived sequences F8, F9, . . . , F15 of the fourthgroup FG2 also differ from one another only by a cyclic shift of theirchip values.

It is to be established furthermore that for each derived sequence ofthe third group FG1 there is a derived sequence of the fourth group FG2,which differs only by an inversion of all of its chip values. If, e.g.,the derived sequence F0 from FG1 is compared with F8 from FG2 in thetable, it is found that all chip values are inverted. Because this alsoapplies to the sequence pairs F1/F9, F2/F10, etc., it is ascertainedthat all derived sequences of the third group FG1 are contained ininverted form in the fourth group FG2:

Ficj=(−1)*Fncj with i=0, 1, . . . , 7, n=i+8 and j=0, 1, . . . , 31.  (4)

In contrast to the PN sequences, in which the corresponding sequencepairs P0/P8, P1/P9 etc. differ by an inversion of each second PN chip,the corresponding pairs F0/F8, F1/F9, etc., from the derived sequencesdiffer by an inversion of all of their chip values.

The properties indicated in the previous approaches of the derivedsequences enable extremely simple realizations of correlation unit 23,evaluation unit 24, and sequence providing unit 25, and therebydetection unit 28 of FIG. 2.

FIG. 3 shows a block diagram of a first exemplary embodiment of thedetection unit of the invention, in which the correlation results areprovided parallel, i.e., substantially simultaneously, and evaluated.Detection unit 30 has a correlation unit (COR) 31 connected todifferential demodulator 22 or equalizer 26 of FIG. 2 and a downstreamevaluation unit (EVAL) 32, as well as a sequence providing unit (SEQ) 33connected to correlation unit 31.

Sequence providing unit 33 has a memory means 34, which is connected tocorrelation unit 31 and whose size is dimensioned in such a way thatprecisely one of the derived sequences can be stored. In the case of thederived sequences F0, F1, F2, . . . , explained with reference to theabove table, memory means 34 is therefore suitable for storing 32 chipvalues. In binary chips, this means a memory space requirement of only32 bits.

Preferably, the memory means is made as a feedback shift register 34with a total of 32 register cells 34-0, 34-1, . . . , 34-31 for storingone chip value each of a derived sequence. In FIG. 3, a state of shiftregister 34 is drawn in by way of example in which the register cells34-0, 34-1, . . . , 34-31 from left to right have the chip value“+++−−−− . . . ” of the derived sequence F0 from the above table(whereby, e.g., the chip value “+1” is saved as a binary one and thechip value “−1” as a binary zero). If the register cells of the shiftregister are now clocked in the chip clock fC=2 MHz (not shown in FIG.3), then the stored content of the register cells per chip periodTC=1/fC=500 ns shifts left by one register cell, so that the derivedsequence F0 is provided at the output of the first register cell 34-0 inthe next 32 chip periods (i.e., in the following symbol periodTS=32*TC). Because of the feedback in the shift register, the shift ofthe content occurs cyclically, which is why the derived sequence F0 thenrepeats in continuous clocking (periodic continuation).

As explained above with reference to the table, the other derivedsequences F1, F2, . . . , F7 of the third group FG1 differ from thederived sequence F0 only by a cyclic shift. The derived sequences F1,F2, . . . , F7 can therefore either be tapped also at the output of thefirst register cell 34-0 (then however beginning later in time than F0)or at the outputs of other register cells (with or without a time offsetin regard to F0).

FIG. 3 shows the register cells at which the other derived sequences F1,F2, . . . , F7 of the third group FG1 are tapped, when they are to beprovided simultaneously, i.e., within the same time interval as thesecond sequence F0. According to the previously explained table, e.g.,the derived sequence F7 begins with a bit pattern that has five timesthe value −1. This bit pattern is evident in the derived sequence F0beginning with the fifth chip, i.e., beginning with the chip F0 c 4. Forthis reason, the feedback shift register 34 of FIG. 3 provides thederived sequences F0 and F7 precisely simultaneously when F7 is tappedat the output of the fifth register cell 34-4 and F0—as alreadydescribed—at the output of the first register cell 34-0. Analogousobservations show that the additional derived sequences F1, F2, . . . ,F6 of the third group FG1 are provided simultaneously at the outputs ofregister cells 34-28, 34-24, 34-20, 34-16, 34-12, or 34-8, as shown inFIG. 3. For the simultaneous provision of the group of eight and derivedsequences F0, F1, . . . , F7, therefore according to FIG. 3, eightoutputs of sequence providing unit 33 are provided, which are connectedto the outputs of register cells 34-0, 34-28, 34-24, 34-20, 34-16,34-12, 34-8, or 34-4.

It is possible in this way by means of a feedback shift register 34having only 32 register cells, which is initialized, e.g., with the chipvalues of the derived sequence F0, to realize an extremely simple andpower-saving sequence providing unit 33, which is suitable for providingall derived sequences F0, F1, . . . , F7 of the third group FG1simultaneously (i.e., without a time offset). According to theinvention, the eight derived sequences F8, F9, . . . , F15 of the fourthgroup FG2 are not provided. This simplifies substantially therealization of correlation unit 31 and evaluation unit 32, as isdescribed in greater detail hereinafter.

Correlation unit 31 has eight multiplier units 35-0, 35-1, . . . , 35-7,each with two inputs and also eight integration units 36-0, 36-1, . . ., 36-7, each downstream of a multiplier unit.

The first inputs of multiplier units 35-0, 35-1, . . . , 35-7 aresupplied with the same signal, namely, the (optionally equalized)demodulated signal s (cf. FIG. 2): s0=s1=s2= . . . =s7=s. The secondinputs of multiplier units 35-0, 35-1, . . . , 35-7 are connected to theoutputs of register cells 34-0, 34-28, 34-24, 34-20, 34-16, 34-12, 34-8,or 34-4 of feedback s register 34, so that they are suppliedsimultaneously (parallel) with the derived sequences F0, F1, . . . , orF7 of the third group FG1.

The operating mode of the i-th branch of the correlation unit will beexplained hereinbelow, whereby i=0, 1, . . . , 7. Multiplier unit 35-imultiplies the values, present in the chip clock fC, of the (optionallyequalized) demodulated signal s with the chip values of the derivedsequence Fi and thus calculates a product signal ti, which in turn hasvalues in the chip clock fC=1/TC. Thus, 32 signal values of the productsignal ti are generated per symbol period TS=32*TC. The downstreamintegration unit 36-i adds per symbol period 31 of these 32 signalvalues of the corresponding product signal ti and thus provides acorrelation result rsFi per symbol period.

During the addition of the 31 signal values, the first signal value ofti in each case—and therefore, the first chip value Fic0 of thecorresponding derived sequence Fi—remains unconsidered in each symbolperiod. In this chip period per symbol period, which is first in regardto time, the integration unit 36-i is set back, and therefore thefollowing integration starts with the value zero.

Based on the differential demodulation, the detection of a current datasymbol requires knowledge of the preceding data symbol. If now—asdescribed above—the correlation results are calculated in all branchesin such a way that the first chip value F0 c 0, F1 c 0, . . . of thederived sequences remain not considered, each data symbol can be decided(detected) advantageously independent of the preceding symbol withoutnotable losses in detection efficiency; this reduces further therealization cost of the detection unit.

As can be derived from the previous description, the signal processingin the individual branches of correlation unit 31 occurs without a timeoffset: all j-th chips of the derived sequences are multiplied with asignal value of s in the same chip period. After the integration,therefore, the correlation results are available simultaneously, i.e.,parallel.

According to the previously described table, the derived sequences canassume antipodal values (+1 and −1). The multiplication of the(optionally equalized) demodulated signal s by the antipodal chip valuesof the derived sequences in this case therefore causes a sign reversalof the values of the demodulated signal s. Therefore, the multiplierunits 35-0, 35-1, . . . 35-7 are advantageously realized as signinverters.

Evaluation unit 32 has a parallel maximum value determination unit (MAX)37, connected to integration units 36-0, 36-1, . . . , 36-7, and adownstream allocation unit (MAP) 38.

Parallel maximum value determination unit 37 compares parallel (i.e.,substantially simultaneously, e.g., in the same chip period) per symbolperiod eight correlation results rsF0, rsF1, . . . , rsF7 in amount withone another and determines the (signed) value of the maximum-valuecorrelation result rsFmax and a sequence index k with integer valuesbetween 0 and 7, which indicates which of the derived sequences F0, F1,. . . , F7 of the third group FG1 is to be assigned to this signedvalue. If, therefore, e.g., the correlation result rsF5 has themaximum-value of all eight correlation results, parallel maximum valuedetermination unit 37 thus determines the signed value rsFmax=rsF5 andthe sequence index k=5, which points to the derived sequence F5.

Allocation unit 38 takes into account the fact that in the correlationunit the correlation was performed only with the eight derived sequencesF0, F1, . . . , F7 of the third group FG1, but not with the eightderived sequences F8, F9, . . . , F15 of the fourth group FG2. Becauseof the above-described property of the derived sequences, according towhich for each derived sequence F0, F1, . . . , F7 of the third groupFG1 there is a derived sequence F8, F9, . . . , F15 of the fourth groupFG2, which differs only by an inversion of all of its chip values, thecorrelation result, e.g., for F13, would differ only by the sign fromthat for F5. For this reason, allocation unit 38 evaluates the sign ofrsFmax.

Allocation unit 38 determines from the sequence index k and the sign ofrsFmax the value of one of the transmitted data symbols d0, d1, . . . Ifthe signed value rsFmax is positive, thus the data symbol value isdetermined that is assigned the sequence from the first PN sequence P0,P1, . . . , P7 of the first group PG1 that is assigned the derivedsequence with the sequence index k, i.e., Fk. If the data symbol valued=5, e.g., is assigned the first PN sequence P5 and this in turn, asdescribed above with reference to the table, the derived sequence F5,allocation unit 38 in the above example thus determines the data symbolvalue as d=k=5, when rsFmax=rsF5>0.

If the signed value rsFmax is negative, however, allocation unit 38 thusdetermines the data symbol value that is assigned the second PN sequenceP8, P9, . . . , P15 of the second group PG2 that is assigned thesequence inverse to the derived sequence with the sequence index k (Fk).If the data symbol value d=13, e.g., is assigned the second PN sequenceP13 and this in turn, as described above with reference to the table,the derived sequence F13=−F5, allocation unit 38 in the above examplethus determines the data symbol value as d=k+8=13, when rsFmax=rsF5≦0.

The exemplary embodiment, described with reference to FIG. 3, of adetection unit of the invention requires only one minimal memory of 32bits, only 8 instead of 16 multiplier units, which are advantageouslymade as sign inverters, only 8 instead of 16 integration units, aparallel maximum value determination unit, and a simple allocation unit.The detection unit is therefore simple to realize and is characterizedby a very low power requirement. A further simplification will bedescribed hereinbelow with reference to FIG. 4.

FIG. 4 shows a block diagram of a preferred second exemplary embodimentof the detection unit of the invention, in which almost all correlationresults are provided serially, i.e., one after another in time, andevaluated. Detection unit 40 has a correlation unit (COR) 41 connectedto differential demodulator 22 or equalizer 26 of FIG. 2 and adownstream evaluation unit (EVAL) 42, as well as a sequence providingunit (SEQ) 43 connected to correlation unit 41.

Correlation unit 41 per symbol period provides the correlation resultsrsF0, rsF1 of the first two branches in the same chip period, whereasthe remaining correlation results rsF2, . . . , rsF7 are each providedin one of the following chip periods. A more cost-effectivedetermination of rsFmax is possible in this way in evaluation unit 42.

Sequence providing unit 43 corresponds substantially to sequenceproviding unit 33 described in reference to FIG. 3. Reference is made inthis respect to the foregoing description. Nevertheless, sequenceproviding unit 43 provides the derived sequence F2 beginning a chipperiod later than the derived sequences F0 and F1, by tapping F2 at theoutput of register cell 34-23 (FIG. 4) instead of 34-24 (FIG. 3), i.e.,a chip period later. The derived sequence F3 is provided one chip periodafter F2 or two chip periods after F0/F1, which is why it is tapped atthe output of register cell 34-18 (FIG. 4) instead of 34-20 (FIG. 3).The outputs of the register cells 34-13, 34-8, 34-3, or 34-30 resultanalogously for the other derived sequences F4, . . . , F7. According toFIG. 4, therefore, eight outputs of providing unit 43 are provided,which are connected to the outputs of register cells 34-0, 34-28, 34-23,34-18, 34-13, 34-8, 34-3, or 34-30, to provide the derived sequences F0and F1 simultaneously and the derived sequences F2, F3, . . . , F7 eachoffset by one chip period.

Because of the almost identical structure, sequence providing unit 43 isalso simple and energy-efficient to realize like sequence providing unit33 described in reference to FIG. 3. Reference is made in this respectto the foregoing description.

Correlation unit 41 also corresponds substantially to correlation unit31 described in reference to FIG. 3. Reference is made in this respectto the foregoing description. Nevertheless, correlation unit 41 has inaddition six delay elements 44-2, 44-3, . . . , 44-7. The delay elementsin this case are arranged in series as a so-called “tapped delay line,”to which the (optionally equalized) demodulated signal s is supplied.Each delay element in this case provides at its output the signal valuesof the signal applied at its input delayed by one chip period, so thatthe demodulated signal s2 delayed by one chip period TC is applied atthe output of the first delay elements 44-2, the demodulated signal s3delayed by two chip periods at the output of the second delay elements44-3, . . . and finally the demodulated signal s7 delayed by six chipperiods at the output of the sixth delay elements 44-7.

The first inputs of the two multiplier units 35-0 and 35-1 of the firsttwo branches (index 0, 1) are supplied directly with the undelayeddemodulated signal s0=s or s1=s, whereas the first inputs of theremaining multiplier units 35-2, 35-3, . . . 35-7 are each connected tothe output of the identically indexed delay element 44-2, 44-3, . . . ,or 44-7, respectively, and thus supplied with the demodulated signal s2,s3, . . . , or s7, respectively, delayed by one, two, . . . , or sixchip periods, respectively. The second inputs of multiplier units 35-0,35-1, . . . , 35-7 are connected to the outputs of register cells 34-0,34-28, 34-23, 34-18, 34-13, 34-8, 34-3, or 34-30 of feedback shiftregister 34, so that they are supplied simultaneously with the derivedsequences F0 and F1 and the derived sequences F2, F3, . . . , F7 delayedrelative to F0/F1 by one, two, . . . , or six chip periods.

These time delays analogously affect the outputs of the correspondingmultiplier units and integration units, so that per symbol period thecorrelation results rsF0 and rsF1 are provided in the same chip periods,whereas the correlation results rsF2, rsF3, . . . , rsF7 are providedwith a time delay of one, two, . . . , or six chip periods.

Alternatively to the arrangement of the delay elements 44-2, 44-3, . . ., 44-7, as shown in FIG. 4, delay elements can also be arranged betweenthe multiplier units and the integration units or, however, (in signalflow direction) after the integration units. Nevertheless, in thesecases a delay by one chip period is necessary in the branch with index2, a delay by two chip periods in the branch with index 3, etc. If thedelay elements are arranged after the integration units, signal valuesthat have a greater bit width than the demodulated signal s must bedelayed in addition.

As described in reference to FIG. 3, the multiplier units shown in FIG.4 are advantageously realized as sign inverters. The integration unitsshown in FIG. 4 also advantageously add per symbol period 31 of the 32signal values of the particular product signal ti.

Evaluation unit 42 has a serial maximum value determination unit 49,connected to integration units 36-0, 36-1, . . . , 36-7, and adownstream allocation unit (MAP) 48.

Serial maximum value determination unit 49 compares serially (i.e., insuccessive chip periods) per symbol period eight correlation resultsrsF0, rsF1, . . . , rsF7 in amount with one another and determines the(signed) value of the maximum-value correlation result rsFmax and asequence index k with integer values between 0 and 7, which indicateswhich of the derived sequences F0, F1, . . . , F7 of the third group FG1is to be assigned to this signed value.

Serial maximum value determination unit 49 has a first multiplexer (MUX)45, whose first input is connected to integration unit 36-0, a secondmultiplexer (MUX) 46 connected input-side to integration units 36-1, . .. , 36-7, and a logic unit (LOG) 47 with two outputs, said unitconnected input-side to the outputs of the two multiplexers 45, 46,whereby the first output of logic unit 47 is connected to the secondinput of first multiplexer 45.

Logic unit 47 is designed in such a way that it compares the inputvalues provided by the two multiplexers 45, 46 in amount and determinesthe signed value of the input value which is higher in amount andprovides it to the first output, and determines the sequence index k ofthe derived sequence to be assigned to this signed value and provides itto the second output. Advantageously, logic unit 47 is formed as a statemachine.

First multiplexer 45 is controlled, e.g., by a control unit in such away that it conducts to its output per symbol period in a specific(“first”) chip period the correlation result rsF0 applied at its firstinput and in the following chip periods the value which is applied atits second input and originates from the first output of logic unit 47.

Second multiplexer 46 is also controlled, e.g., by the aforementionedcontrol unit in such a way that it conducts to its output in theaforementioned “first” chip period the correlation results rsF1 appliedat its first input, in the following chip period the correlation resultrsF2 applied at its second input, etc.

The correlation results rsF0 and rsF1 are compared with one another inamount in this way per symbol period in the aforementioned “first” chipperiod and as the result the signed value of the correlation result thatis greater in amount and the value of the sequence index k aredetermined, which indicates whether F0 (then: k=0) or F1 (then: k=1) isto be assigned to this signed value. During the following chip period,the correlation result rsF2 is then compared with the result determinedin the preceding chip period and as the new results the signed valuethat has the higher amount, and the value of the sequence index k aredetermined, which indicates whether F0 or F1 or F2 is to be assigned tothis signed value. In the following chip periods, then in each case oneof the correlation results rsF3, . . . , rsF7 is compared with theresults determined in the preceding chip period and as the new resultthe signed value that has the higher amount, and the value of thesequence index k of the derived sequence that is to be assigned to thesigned value are determined, until all correlation results areconsidered and thus the signed value of the maximum-value correlationresult rsFmax and the sequence index k, which indicates which of theeight derived sequences F0, F1, . . . , F7 is to be assigned this signedvalue rsFmax, are determined.

Allocation unit 48 corresponds to allocation unit 38 described inreference to FIG. 3. Reference is made in this respect to the foregoingdescription.

The exemplary embodiment, described with reference to FIG. 4, of thedetection unit of the invention requires only a minimal memory of 32bits, only 8 instead of 16 multiplier units, which are advantageouslymade as sign inverters, only 8 instead of 16 integration units, a serialmaximum value determination unit which is very simple to realize, and alikewise very simple allocation unit. The detection unit is thereforevery simple to realize and is notable for an extremely low powerrequirement.

FIG. 5 shows an alternative realization form of the sequence providingunit. Sequence providing unit 53 has a total of eight multiplexers (MUX)52-0, 52-1, . . . , 52-7, whose control input is connected in each caseto counting unit (CNT) 51. Whereas the derived sequences F0, F1, . . . ,F7 are provided at the outputs of the multiplexers, the 32 inputs permultiplexer have fixed values (such as, e.g., of the supply voltage andground), which represent the specific derived sequence. In analogy tothe “current” content of the register cells 34-0, . . . , 34-31 of shiftregister 34 from FIGS. 3 and 4, the input values of multiplexers 52-0,52-1, . . . , 52-7 in FIG. 5 are represented by plus and minus symbols.In this case, the sequence “+++−−−−− . . . −”, drawn from top to bottomat the inputs of multiplexer 52-0 in FIG. 5, corresponds to thesequence, drawn from left to right in shift register 34 of FIG. 3 inregister cells 34-0, . . . , 34-31, and thereby the derived sequence F0.In analogy, the sequence “++−−+++− . . . −”, drawn at the inputs ofmultiplexer 52-1 in FIG. 5, corresponds to the sequence, drawn inregister cells 34-28, . . . , 34-31, 34-0, . . . , 34-27 in FIG. 3, andthereby the derived sequence F1, etc. Whereas the plus and minus symbolsin the register cells of FIGS. 3 and 4 represent the currently storedvalue, in FIG. 5 the plus symbol, e.g., represents a connection to thesupply voltage and the minus symbol a connection to ground.

Counting unit 51 is formed to count from zero to 31 in the chip clock fCand then to begin again at 0. It therefore provides at its output persymbol period a running chip index (0 . . . 31). In the first chipperiod (with index zero), therefore, the multiplexers each conduct thevalue applied at its first (topmost) input to their output, so that inthe first chip period the first chip values of the derived sequences areprovided simultaneously (F0 c 0, F1 c 0, . . . , F7 c 0). In the nextchip periods, the multiplexers each conduct synchronously the valuesapplied at their second, third, etc., inputs, until after all 32 chipperiods all derived sequences are provided parallel. Because theprovision of the derived sequences occurs without a time offset relativeto one another, the sequence providing unit 53 of FIG. 5 can be useddirectly instead of sequence providing unit 33 in FIG. 3.

By means of a simple modification, sequence providing unit 53 of FIG. 5can be used instead of sequence providing unit 43 in FIG. 4. For thispurpose, only the input values of multiplexers 52-2, 52-3, . . . , 52-7are to be shifted cyclically; i.e., the inputs of the aforementionedmultiplexers are to be wired cyclically shifted. The input values ofmultiplexer 52-2 are hereby to be shifted cyclically downward in FIG. 5by one input position, that of multiplexer 52-3 downward by two inputpositions, etc., and that of multiplexer 52-7 downward by six inputpositions. In this way, the derived sequences are provided seriallyanalogously to sequence providing unit 43 of FIG. 4, i.e., the derivedsequences F0 and F1 in the same chip period, F2 beginning one chipperiod later, F3 beginning another chip period later, etc. Instead ofthe preferred cyclic shift of the input values of multiplexers 52-2,52-3, . . . , 52-7, of course, the output values of counting unit 51, assupplied to said multiplexers, can be delayed accordingly.

The detection unit of the invention described heretofor with referenceto FIGS. 2 to 5 and thereby also transmitting/receiving devices, whichhave this type of detection unit, are notable for a very simplerealizability, an extremely low power requirement, and a high efficiency(bit error rate or the like depending on interfering effects such asnoise and/or channel distortions). According to tests performed by theapplicant, the digital parts of the receiving units—without asynchronization unit—require a hardware effort on the order of a fewthousand gate equivalents (NAND gates with two inputs). In the datatransmission mode, these digital parts of the receiving units have apower requirement on the order of a few milliwatts (mW).

Although the present invention was described above with reference toexemplary embodiments, it is not limited thereto but can be modified inmany ways. Thus, the invention is not limited either to WPANs or toWPANs according to IEEE 802.15.4 or to the PN sequences specifiedtherein (number and length of the sequences, number of levels and valuesof the chips, etc.), rates and number of levels of thechips/symbols/bits, etc. The invention is also not limited to thederived sequences given in the aforesaid table. Various equivalentlogical relationships can be given for the relationship between thederived chips and the PN chips.

LIST OF REFERENCE CHARACTERS

-   10 data transmission system/“Wireless Personal Area Network” (WPAN)    according to the IEEE Standard 802.15.4-   11-13 Transmitting/receiving device, “transceiver”-   14 antenna-   15 transmitting unit, “transmitter”-   16 receiving unit, “receiver”-   17 control unit-   21 internal receiver-   22 differential demodulator-   23 correlation unit, despreader-   24 evaluation unit, detector-   25 sequence providing unit-   26 equalizer-   28, 30 detection unit-   31 correlation unit-   32 evaluation unit, detector-   33 sequence providing unit-   34 memory means; shift register-   34-0, 34-1, . . . register cell 0 or 1 . . . of the shift register-   35-0, 35-1, . . . multiplier unit 0 or 1 . . .-   36-0, 36-1, . . . integration unit 0 or 1 . . .-   37 parallel maximum value determination unit-   38 allocation unit-   40 detection unit-   41 correlation unit-   42 evaluation unit, detector-   43 sequence providing unit-   44-2, 44-3, . . . delay element 2 or 3 . . .-   45, 46 first or second multiplexer-   47 logic unit-   48 allocation unit-   49 serial maximum value determination unit-   51 counting unit-   52-0, 52-1, . . . multiplexer 0 or 1 . . .-   53 sequence providing unit-   CNT counting unit-   COR correlation unit, despreader-   DEMOD differential demodulator-   EQ equalizer-   EVAL evaluation unit, detector-   IC integrated circuit; chip-   iREC internal receiver-   ISM industrial, scientific, medical (2.4 GHz frequency band)-   LOG logic unit-   MAP allocation unit-   MAX maximum value determination unit-   MUX multiplexer-   PN pseudo-noise-   QPSK quadrature phase shift keying-   RX receiving unit, receiver-   SEQ sequence providing unit-   TRX transmitting/receiving device, transceiver-   TX transmitting unit, transmitter-   WPAN wireless personal area network-   b complex baseband signal with sampling values in the chip clock-   d0, d1, d2, . . . data symbols-   fB bit clock (=1/TB)-   fC chip clock (=1/TC)-   fS symbol clock (=1/fS)-   F0, F1, F2, . . . derived sequences, F-/FSK sequences, second codes    (receive-side)-   F5 c 0, F5 c 1, chips of the derived sequence (“derived chips”) F5-   FG1 third group of derived sequences F0, . . . , F7-   FG2 fourth group of derived sequences F8, . . . , F15-   i, j, k indexes-   n number of the (derived) sequences in the third group-   P0, P1, P2, . . . PN sequences, spreading sequences, first codes    (transmit-side)-   P0, P1, . . . , P7 first PN sequences-   P8, P9, . . . , P15 second PN sequences-   P5 c 0, P5 c 1, . . . chips of the PN sequence (“PN chips”) P5-   PG1 first group of first PN sequences P0, . . . , P7-   PG2 second group of second PN sequences P8, . . . , P15-   r radio signal, incoming signal-   rsF0, rsF1, . . . correlation results-   rsFmax maximum-value correlation result (signed)-   s differentially demodulated (and optionally equalized) signal;    soft-information values-   s0, s1, . . . signal values of the signal s present in the chip    clock-   t0, t1, . . . product signals-   TB bit period (=1/fB)-   TC chip period (=1/fC)-   TS symbol period (=1/fS)

1. A detection unit (28; 30; 40) for detecting data symbols (d0, d1, . .. ) which are contained in a differentially demodulated signal (s) andto which transmit-side in each case a PN sequence (P0, P1, . . . P15)from a sequence set can be assigned, which has a first group (PG1) offirst PN sequences (P0, P1, . . . , P7) and a second group (PG2) ofsecond PN sequences (P8, P9, . . . , P15), whereby the first and secondPN sequences within their respective group differ from one another onlyby a cyclic shift in their chip values and whereby the second group(PG2) for each first PN sequence (P0) has a corresponding second PNsequence (P8), which differs from the first PN sequence (P0) only by aninversion of each second chip value, comprising: a) sequence providingunit (25; 33; 43; 53), which is formed to provide a third group (FG1) ofderived sequences (F0, F1, . . . , F7), whereby the third group (FG1)for each first PN sequence (P0) has a derived sequence (F0), which isassigned to said first PN sequence (P0) and can be derived therefrom bymeans of logic operations, but is not identical thereto, and whereby thederived sequences (F0, F1, . . . , F7) of the third group (FG1) differfrom one another only by a cyclic shift in their chip values, b) acorrelation unit (23; 31; 41) which is connected to the sequenceproviding unit (25; 33; 43; 53) and is formed to calculate correlationresults (rsF0, rsF1, . . . , rsF7) by correlating the differentiallydemodulated signal (s) with each derived sequence (F0, F1, . . . , F7)of the third group (FG1), and c) an evaluation unit (24; 32; 42) whichis connected to the correlation unit (23; 31; 41) and is formed toderive the values of the data symbols (d0, d1, . . . ) by evaluating thecorrelation results (rsF0, rsF1, . . . , rsF7).
 2. The detection unit(28; 30; 40) according to claim 1, characterized in that the sequenceproviding unit (25; 33; 43) has precisely one memory means (34), whichis formed to store precisely one of the derived sequences (F0, F1, . . ., F7) of the third group (FG1).
 3. The detection unit (28; 30; 40)according to claim 2, characterized in that the memory means has afeedback shift register (34).
 4. The detection unit (28; 30; 40)according to claim 3, characterized in that means are provided forclocking the feedback shift register (34) in the chip clock (fC) and thesequence providing unit (25; 33; 43) is formed to provide the derivedsequences (F0, F1, . . . , F7) of the third group (FG1) at the outputsof the specific register cells (34-0, 34-28, . . . ) of the feedbackshift register (34).
 5. The detection unit (28; 30; 40) according toclaim 1, characterized in that the sequence providing unit (25; 53) hasa counting unit (51) and multiplexers (52-0, 52-1, . . . ) connected tothe counting unit (51), whereby fixed values can be applied at theinputs of the multiplexers and the sequence providing unit (25; 53) isformed to provide the derived sequences (F0, F1, . . . , F7) of thethird group (FG1) at the outputs of the multiplexers (52-0, 52-1, . . .).
 6. The detection unit (28; 30; 40) according to claim 1,characterized in that the third group (FG1) has at least two derivedsequences (F0, F1, . . . , F7) and their number n coincides with thenumber of the first PN sequences (P0, P1, . . . , P7) in the first group(PG1) and with the number of the second PN sequences (P8, P9, . . . ,P15) in the second group (PG2).
 7. The detection unit (28; 30; 40)according to claim 6, characterized in that the correlation unit (23;31; 41) has the following units: a) n multiplier units (35-0, 35-1, . .. ), each connected to the sequence providing unit (25; 33; 43; 53), forcalculating n product signals (t0, t1, . . . ) by multiplying signalvalues (s0, s1, . . . ), present in the chip clock (fC), of thedemodulated signal (s) by chip values in each case of one of the derivedsequences (F0, F1, . . . ) of the third group (FG1), and b) nintegration units (36-0, 36-1, . . . ), each connected to one of themultiplier units (35-0, 35-1, . . . ), to provide n correlation results(rsF0, rsF1, . . . , rsF7) per symbol period (TS) by adding a number ofsignal values in each case of one of the n product signals (t0, t1, . .. ).
 8. The detection unit (28; 30; 40) according to claim 7, wherebythe multiplier units (35-0, 35-1, . . . ) consist of means for signreversal.
 9. The detection unit (28; 30; 40) according to claim 7,wherein the integration units (36-0, 36-1, . . . ) are formed to add anumber of signal values that is smaller by one than the number of chips(F5 c 0, F5 c 1, F5 c 2, . . . ), which has each derived sequence (F5).10. The detection unit (28; 30) according to claim 7, characterized inthat the evaluation unit (24; 32) is formed to evaluate in parallel ncorrelation results (rsF0, rsF1, . . . , rsF7) per symbol period (TS) byevaluating these n correlation results (rsF0, rsF1, . . . , rsF7)substantially simultaneously.
 11. The detection unit (28; 30) accordingto claim 10, characterized in that the evaluation unit (24; 32) has thefollowing units: a) a parallel maximum value determination unit (37),which is connected to the integration units (36-0, 36-1, . . . ) and isformed to compare the n correlation results (rsF0, rsF1, . . . , rsF7)with one another substantially simultaneously in amount and to determineas the result the signed value of the maximum-value correlation result(rsFmax) and a sequence index (k), which indicates which of the nderived sequences (F0, F1, . . . , F7) is to be assigned to said signedvalue, and b) an allocation unit (38), which is connected to theparallel maximum value determination unit (37) and is formed todetermine a value of one of the data symbols (d0, d1, . . . ) from thesequence index (k) and the sign of the signed value of the maximum-valuecorrelation result (rsFmax).
 12. The detection unit (28; 40) accordingto claim 7, characterized in that a) the third group (FG1) has at leastfour derived sequences (F0, F1, . . . ), b) the correlation unit (23;41) has delay elements (44-2, 44-3, . . . ), which are arranged in sucha way that per symbol period (TS) two first results (rsF0, rsF1) of then correlation results are provided in the same chip period and n-2second results (rsF2, . . . , rsF7) of the n correlation results in thefollowing chip periods, c) the evaluation unit (24; 42) is formed toevaluate serially the n correlation results (rsF0, rsF1, . . . ) persymbol period (TS) by evaluating the first correlation results (rsF0,rsF1) during a first chip period and one each of the second correlationresults (rsF2, . . . , rsF7) during the following chip periods.
 13. Thedetection unit (28; 40) according to claim 12, characterized in that thedelay elements (44-2, 44-3, . . . ) are arranged in the signal pathupstream of the multiplier units (35-0, 35-1, . . . ).
 14. The detectionunit (28; 40) according to claim 12, characterized in that theevaluation unit (24; 42) has the following units: a) a serial maximumvalue determination unit (49), which is connected to the integrationunits (36-0, 36-1, . . . ) and is formed to compare the firstcorrelation results (rsF0, rsF1) in amount with one another during thefirst chip period and to determine as the result the signed value of thefirst correlation result that has the highest amount, and a sequenceindex (k) which indicates which of the derived sequences (F0, F1, . . ., F7) is to be assigned to this signed value, in the following chipperiods, to compare one each of the second correlation results (rsF2, .. . , rsF7) in amount with the result determined in each case during thepreceding chip period and to determine as the result the signed valuethat has the highest amount, and a sequence index (k) which indicateswhich of the derived sequences (F0, F1, . . . , F7) is to be assigned tothis signed value, to perform the preceding step so often until allsecond correlation results (rsF2, . . . , rsF7) are considered and thusthe signed value of the maximum-value correlation result (rsFmax) and asequence index (k) are determined, which indicates which of the nderived sequences (F0, F1, . . . , F7) is to be assigned to this signedvalue, and b) an allocation unit (48), which is connected to the serialmaximum value determination unit (49) and is formed to determine a valueof one of the data symbols (d0, d1, . . . ) from the sequence index (k)and the sign of the signed value of the maximum-value correlation result(rsFmax).
 15. The detection unit (28; 40) according to claim 14,characterized in that the serial maximum value determining unit (49) hasthe following units: a) a first multiplexer (45), which is connected toa first integration unit (36-0) and is controlled in such a way that itconducts to its output during the first chip period the firstcorrelation result (rsF0) applied at its first input and in thefollowing chip periods the value applied at its second input, b) asecond multiplexer (46), which is connected to n-1 second integrationunits (36-1, 36-2, . . . ) and is controlled in such a way that itconducts to its output during the first chip period the firstcorrelation result (rsF1) applied at its inputs and in the followingchip periods one each of the second correlation results (rsF2, . . . ,rsF7) applied at its other inputs, c) a logic unit (47) having twooutputs and connected to the outputs of the two multiplexers (45, 46),whereby the first output is connected to the second input of the firstmultiplexer (45) and the logic unit is designed in such a way that itcompares the values in amount conducted by the two multiplexers (45, 46)and determines the signed value of the higher value in amount andprovides it at the first output, and determines the sequence index (k)of the sequence to be assigned to said signed value and provides it atthe second output.
 16. The detection unit (28; 40) according to claim15, wherein the logic unit (47) has a state machine.
 17. The detectionunit (28; 30; 40) according to claim 11, wherein the allocation unit(38; 48) is formed to determine the value of one of the data symbols(d0, d1, . . . ) a) to which the first PN sequence (P0, P1, . . . , P7)of the first group (PG1) is to be assigned that is assigned the derivedsequence (Fk) with the sequence index (k), if the signed value of themaximum-value correlation result (rsFmax) is positive, and otherwise b)to which the second PN sequence (P8, P9, . . . , P15) of the secondgroup (PG2) is assigned that is assigned the sequence inverse to thederived sequence (Fk) with the sequence index (k).
 18. The detectionunit (28; 30; 40) according to claim 1, wherein each derived sequence(F5) has derived chips (F5 c 0, F5 c 1, F5 c 2, . . . ), whose values ineach case of a logic operation of the particular PN chips (P5 c 0, P5 c1, P5 c 2, . . . ) correspond to the first PN sequence (P5) assigned thederived sequence (F5).
 19. The detection unit (28; 30; 40) according toclaim 18, characterized in that the derived chips with a first positiveindex (F5 ci, i=1, 2, . . . ) each have a value that can be derived froman XOR operation of the PN chip with said first positive index (P5 ci,i=1, 2, . . . ) with the PN chip preceding index-wise (P5 cj, j=i−1).20. The detection unit (28; 30; 40) according to claim 18, characterizedin that the index-wise first derived chip (F5 c 0) has a value that canbe derived from an XOR operation of the index-wise first PN chip (P5 c0) with the index-wise last PN chip (P5 c 31),
 21. The detection unit(28; 30; 40) according to claim 19, characterized in that a) the derivedchips with an even index (F5 c 0, F5 c 2, . . . ) each have a value thatis assigned to the value of the respective XOR operation and b) thederived chips with an odd index (F5 c 1, F5 c 3, . . . ) each have avalue that is assigned to the inverted value of the respective XORoperation.
 22. A transmitting/receiving device (11-13), particularly fora data transmission system (10) according to the IEEE Standard 802.15.4in the 2.4 GHz band, comprising a) an antenna (14), b) a transmitterunit (15) connected to the antenna (14) to transmit data particularlyaccording to the IEEE Standard 802.15.4 in the 2.4 GHz band, wherein thetransmitting unit (15) is formed to assign to each data symbol (d0=5) aPN sequence (P5) from a sequence set, which has a first group (PG1) offirst PN sequences (P0, P1, . . . , P7) and a second group (PG2) ofsecond PN sequences (P8, P9, . . . , P15), whereby the first and secondPN sequences within their respective group differ from one another onlyby a cyclic shift in their chip values and whereby the second group(PG2) have for each first PN sequence (P0) a corresponding second PNsequence (P8), which differs from the first PN sequence (P0) only by aninversion of every second chip value, c) a receiving unit (16),connected to the antenna (14), with a differential demodulator (22) anda detection unit (28; 30; 40) according to anyone of claims 1 through21, d) a control unit (17), connected to the transmitting unit (15) andthe receiving unit (16), for controlling the transmitting unit (15) andthe receiving unit (16).
 23. An integrated circuit, particularly for atransmitting/receiving device according to claim 22, having a detectionunit (28; 30; 40) according to claim 1.